1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same.
2. Description of the Related Art
As nonvolatile memories capable of storing information even after the power therefore is turned off, a flash memory and a ferroelectric memory are known.
Among these memories, the flash memory contains a floating gate buried in a gate insulating film of an insulated gate field-effect transistor (IGFET), and stores information by accumulating electric charges indicating memory information in the floating gate. However, this type of the flash memory has a drawback of requiring relatively high voltages, since tunnel currents should flow through the gate insulating film in writing and deleting of the information.
On the other hand, the ferroelectric memory, which is also called FeRAM (Ferroelectric Random Access Memory), stores the information by utilizing a hysteresis property of a ferroelectric film provided in a ferroelectric capacitor. The ferroelectric film causes polarization in accordance with an electric voltage applied between a lower electrode and an upper electrode of the capacitor, and spontaneous polarization remains even after the applied electric voltage is removed. If polarity of the applied electric voltage is reversed, this spontaneous polarization is also reversed. Subsequently by setting directions of the spontaneous polarization corresponding to “1” and “0,” the information is written into the ferroelectric film. The FeRAM has advantages that an electric voltage required for writing information is lower than that of the flash memory, and that writing can be performed at a higher speed than that of the flash memory.
In the FeRAM, spaces between wirings and those between adjacent capacitors have been becoming narrower and narrower in response to miniaturization of semiconductor devices in recent years.
While the spaces between wirings and between capacitors in the FeRAM have to be filled with an insulating film such as silicon oxide film, there is a risk of causing voids in the insulating film in the aforementioned narrow spaces if a gap-filling property of the insulating film is inadequate.
In response, a silicon oxide film having an excellent gap-filling property, which is formed by an HDP (High Density Plasma) CVD method, has been used as the insulating film for the FeRAM in recent years.
FIG. 1 is a schematic diagram for explaining a reason why the gap-filling property are enhanced in the HDPCVD method.
In an example shown in FIG. 1, a silicon oxide film 113 is formed on metal wirings 112 by using SiH4 (silane), O2 (oxygen) and Ar (argon) as a film deposition gas in the HDPCVD method. In the HDPCVD method, while a high-frequency plasma-generating electric power, which makes the film deposition gas into plasma, is applied from above a silicon substrate 111, a high-frequency bias electric power is applied from under the silicon substrate 111.
The high-frequency bias electric power serves to pull oxygen radicals and argon ions toward the substrate in a film deposition atmosphere. Therefore, a process of film deposition and a process of sputter-etching by the radicals and ions are simultaneously performed in the HDPCVD method. As such, the silicon oxide film 113 on shoulders 112b of the metal wirings 112 is scraped off by the sputter-etching, which thereby makes possible to prevent the formation of overhanging portions 113a of the silicon oxide film 3 in the vicinities of the shoulders 112b. As a result, it becomes possible to preferably embed the silicon oxide film 113 in the narrow spaces between each of the metal wiring 112 while inhibiting the voids from occurring in these spaces.
Patent Literature 1 discloses a silicon oxide film formed by the above-described HDPCVD method for an insulating film of filling spaces between adjacent ferroelectric capacitors.
In addition to the Patent Literature 1, technologies related to the present application is disclosed in Patent Literatures 2 to 4.
Among these literatures, Patent Literature 2 discloses a film deposition method including two steps, in which a substrate position is changed in an ECR (electron cyclotron resonance) plasma CVD apparatus
Additionally, Patent Literature 3 discloses that three insulating films are laminated by changing their deposition condition in the ECR plasma CVD apparatus.
Furthermore, Patent Literature 4 discloses that void-free thin film is formed on a stepped substrate by alternately repeating a sputter-etching and film deposition utilizing a capacitively coupled discharge in the plasma CVD apparatus    [Patent Literature 1] Japanese Patent No. 3482199 Specification    [Patent Literature 2] Japanese Patent No. 2913672 Specification    [Patent Literature 3] Japanese Patent No. 2819774 Specification    [Patent Literature 4] Japanese Patent No. 3080843 Specification
Incidentally, a capacitor dielectric film constituting the ferroelectric capacitor of the FeRAM is formed of a metal oxide or the like. Therefore, the capacitor dielectric film is easily deoxidized and brought into an oxygen deficient state when it is exposed to a reducing atmosphere which contains hydrogen, moisture, and the like. The capacitor dielectric film in the oxygen deficient state exhibits poor ferroelectric property. Accordingly, it is important how to prevent the capacitor dielectric film from being reduced in the manufacturing processes of the FeRAM. This is also the case where the HDPCVD method is employed in the manufacturing processes of the FeRAM.